This may be a repeat, my apologies if it is, my server told me the first
version was "undeliverable".
*BLOWING UP A GARBAGE CAN USING A SODA BOTTLE AND LIQUID NITROGEN.***
*The soda bottle.***
A 2 liter soda bottle works well, although I have used smaller bottles,
e.g. 1 liter Seltzer bottles. The newer "reduced plastic" water bottles
will work, but produce a less energetic explosion as the bottle bursts
more easily than the thicker walled bottles. Recycled bottles are fine,
but, as I recently discovered, they should not have liquid nitrogen,
LN2, put in them until the demonstration is performed. I thought that
putting a desert spoon of LN2 in bottles before shipping them would
prevent them from damage when shipping. It turns out, as far as I can
tell, that this actually weakens the bottle and causes it to leak at the
site where the plastic is injected, rather than exploding. A friend of
mine who works for Pepsi Cola assures me that this is the weakest point
on the bottle. I'm fortunate that both Pepsi Cola and Coca Cola are
willing to donate virgin bottles (never had soda in them, nor a label on
them) to me. I have never had one of either of these brand's new bottles
fail. The lid of the bottle needs to be screwed on tightly, but be
careful not to over tighten it and strip the screw threads. I usually
take the plastic ring off the bottle cap before use. I use a small
funnel to pour about 300 mL (about a cup) of LN2 in the bottle. I do not
wear gloves while doing this. It seems that using more nitrogen makes it
take a longer time for the bottle to explode, although I have not timed
how long varying amounts take. I have timed it a few times for
approximately 300 mL and it took about six minutes usually.
*The garbage can.***
If you do this outdoors you can just let the "naked" bottle explode, but
I would very strongly recommend that you do not do this. The frozen
shards of plastic especially the section around the cap of the bottle
constitute dangerous shrapnel, but if you insist on doing it this way,
no one should be within 100 meters of the bottle when it does explode.
To make this demonstration safer I place the bottle under an inverted
plastic, never metal, garbage can. I have found the smooth sided 44
gallon BRUTE cans by Rubbermaid work well and have a longer life
expectancy than thinner cans or ones with folds in the plastic.
To extend the life of them, these days I cut off the bottom ten
centimeters of an old can that has holes or splits in its sides and put
that inside the bottom of the new can and duct tape it in place. Without
this a can seems to last for about ten explosions before the bottom
ruptures, with the reinforcement the can last three to four times as
long and it is usually splits in the side that cause its demise. Small
slits in the side of a can may be repaired with a large patch cut from
an old can duct taped inside the new can.
Just having a can over the bottle however does not ensure safety, as
some of the bottle pieces can still escape from under the can. The cap
and neck of the bottle are particularly nasty shrapnel. To prevent them
from escaping and to direct the rest of the bottle up into the can, I
use a base to hold the bottle.
Figure 4. Base for exploding soda bottle, drawing.
To make this base fasten a stainless steel mixing bowl to a two inch
thick piece of plank, both of which have a four centimeter hole cut
centrally in them. As can be seen in Figure 3. I reinforced the bowl
where it fastens to the wood with a large washer held in place by
smaller washers on the bolts. This assembly is in turn is fastened to
two pieces of plywood. Bolts hold all of this together, as they do not
pull out as easily as wood screws.
The resulting explosion is quite spectacular, the bowl tends to direct
the gas upward resulting in the can being launched about 20 meters into
the air, see figure 5.
Notice the piece of green soda bottle to the right of the garbage can.
If the demonstration is done on level ground the can usually lands
within about ten meters of the launch position. I have placed the whole
arrangement on a sheet of inch thick plywood, angled to the horizontal
to direct the can away from the audience.
For indoor shows I tie one handle of the barrel to some relatively
immovable object, e.g. a door knob, stair hand rail, or even the
concrete block later to be broken on me. I make the rope short enough so
that the barrel can neither hit an audience member, nor any breakable
objects, e.g. ceiling tiles, or the other apparatus.
Outdoors I sometimes use an alternative to the bowl, which launches the
can even higher. This base is made from a piece of eighth inch thick,
six inch diameter, eight inch long brass cylinder, surrounding a
sixteenth inch thick, sixteen inch long aluminum cylinder. Both
cylinders were salvaged from scrapped equipment.
The aluminum tube fits inside the brass tube. The screws at the bottom
fasten both tubes to a two inch thick, six inch diameter piece of wood,
in turn fastened to a piece of plywood. Sometimes I line the inside of
the tubes with a plastic trash bag and then pour in about half a gallon
of water. This reduces the time for the bottle to explode from about six
minutes to less than one minute usually.
I recently measured the sound pressure level at a distance of 3.5 meters
from the garbage can, using a Model 370 Triplett sound pressure level
meter. For a 2 liter, fluted bottom Coke bottle, filled with about 300
mL of LN2, the reading was 105 ± 1 dB. From what I read, this is not a
dangerous level for a sound of short duration. I still recommend that
parents with babies or very young children sit considerably further
away. Startled children are no fun for anyone.
I hope that this may be of some use to some of you. If you have
questions I may be reached at dwilley@pitt.edu